High energy electron impact ionization for elemental analysis by energy dispersive X-ray spectrometry

A method has been demonstrated in which the emission of characteristic X-rays following impact ionization by electrons of several MeV energy is used for quantitative elemental analysis. Because of the unique properties of MeV electrons with respect to their X-ray production yield and range in solids, the method has comparable sensitivity over a wide range of elements and relatively less stringent sample preparation requirements. By using energy dispersive techniques to detect the X-rays, a simultaneous determination of the weight fraction of the elements in an unknown sample is possible from a procedure based entirely on empirically determined relative X-ray yields. The method was tested by analyzing three standard metal alloy samples obtained from the National Bureau of Standards. Elements reaging from iron (Z=26) to lead (Z=82) with concentrations from 0.06% to 88% were quantitatively determined. In general, good approximate agreement was found wit the reported assays even for the minor constituents.     

Structure and Electronic Properties of Extended Chromophores for Applications in Second-Order Nonlinear Optics

A structural and theoretical analysis of new 2-[(4-phenylazo)phenyl] benzoxazole chromophores of potential interest in the field of second-order nonlinear optics is presented. Computations predict comparatively high hyperpolarizabilities for most of the compounds in their equilibrium nuclear configuration, with a significant dependence upon some conformational degrees of freedom and independence upon some others. This behavior is rationalized in the frame of the two-level model and sheds light on the conjugation pattern of these new chromophores.     

Enthalpies of transfer from water to methanol of cations complexed with 18-crown-6

Enthalpies of transfer from water to methanol have been obtained via a thermochemical cycle for the [M⁺18C6] complexes where M⁺  Na⁺, K⁺, Rb⁺, Cs⁺, and Ag⁺. Variation of the transfer enthalpy with M⁺ is small.     

High trans selectivity in the copper bis(oxazoline)-catalyzed asymmetric cyclopropanation of olefins by (trimethylsilyl)diazomethane

Copper(I) bis(oxazoline) species are among the most enantioselective cyclopropanation catalysts that have been reported, although these catalysts generally give low diastereoselectivities. We have observed greatly improved diastereoselectivities using (trimethylsilyl)diazomethane as the carbon source. We have also identified several bis(oxazoline) species that also give comparable or higher enantioselectivities with (trimethylsilyl)diazomethane compared to the more readily available ethyl diazoacetate. The application of this methodology to several olefins has been explored.     

Facile synthesis of 5-(α-alkyl-substituted) furans

2-Halo, 2-hydroxy- or 2-alkoxyalkyl substituted furans are easily synthesized under acidic conditions by intramolecular cyclization of α,β-unsaturated 1,4-diketones by a simple and cheap procedure. Some aspects of the mechanism are discussed.     

Partition coefficients for the SAMPL5 challenge using transfer free energies

SAMPL challenges (Mobley et al. in J Comput Aided Mol Des 28:135–150, 2014; Skillman in J Comput Aided Mol Des 26:473–474, 2012; Geballe in J Comput Aided Mol Des 24:259–279, 2010; Guthrie in J Phys Chem B 113:4501–4507, 2009) provide excellent opportunities to assess theoretical approaches on new data sets with a goal of gaining greater insight towards protein and ligand modeling. In the SAMPL5 experiment, cyclohexane–water partition coefficients were determined using a vertical solvation scheme in conjunction with the SMD continuum solvent model. Several DFT functionals partnered with correlation consistent basis sets were evaluated for the prediction of the partition coefficients. The approach chosen for the competition, a B3PW91 vertical solvation scheme, yields a mean absolute deviation of 1.9 logP units and performs well at estimating the correct hydrophilicity and hydrophobicity for the full SAMPL5 molecule set.     

Postprandial metabolomics: A pilot mass spectrometry and NMR study of the human plasma metabolome in response to a challenge meal

The study of postprandial metabolism is relevant for understanding metabolic diseases and characterizing personal responses to diet. We combined three analytical platforms – gas chromatography-mass spectrometry (GC-MS), liquid chromatography-mass spectrometry (LC-MS) and nuclear magnetic resonance (NMR) – to validate a multi-platform approach for characterizing individual variation in the postprandial state. We analyzed the postprandial plasma metabolome by introducing, at three occasions, meal challenges on a usual diet, and 1.5 years later, on a modified background diet. The postprandial response was stable over time and largely independent of the background diet as revealed by all three analytical platforms. Coverage of the metabolome between NMR and GC-MS included more polar metabolites detectable only by NMR and more hydrophobic compounds detected by GC-MS. The variability across three separate testing occasions among the identified metabolites was in the range of 1.1–86% for GC-MS and 0.9–42% for NMR in the fasting state at baseline. For the LC-MS analysis, the coefficients of variation of the detected compounds in the fasting state at baseline were in the range of 2–97% for the positive and 4–69% for the negative mode. Multivariate analysis (MVA) of metabolites detected with GC-MS revealed that for both background diets, levels of postprandial amino acids and sugars increased whereas those of fatty acids decreased at 0.5 h after the meal was consumed, reflecting the expected response to the challenge meal. MVA of NMR data revealed increasing postprandial levels of amino acids and other organic acids together with decreasing levels of acetoacetate and 3-hydroxybutanoic acid, also independent of the background diet. Together these data show that the postprandial response to the same challenge meal was stable even though it was tested 1.5 years apart, and that it was largely independent of background diet. This work demonstrates the efficacy of a multi-platform metabolomics approach followed by multivariate and univariate data analysis for a broad-scale screen of the individual metabolome, particularly for studies using repeated measures to determine dietary response phenotype.     

Chlorobis(nitrato‐O,O')(tetraethylene glycol dimethyl ether)neodymium(III), [NdCl(NO3)2(tetraglyme)]: A Novel Heteroleptic Complex

In the crystal structure of [NdCl(NO₃)₂(tetraglyme)] (triclinic, P1, Z = 2, a = 7.814(1); b = 7.9832(9); c = 15.322(2) Å; α = 87.38(1); β = 84.88(1); γ = 79.83(1)°), neodymium is ten coordinate with two transoid chelating nitrate ligands, a chlorine and the five oxygen atoms of the tetraglyme ligand in an irregular array.     

Das gemischtvalente ternäre Oxoferrat(II,III) K3[Fe2O4] – eine aufgefüllte Variante des K2[Fe2O4]‐Typs

The Mixed‐Valent Oxoferrate(II,III) K₃[Fe₂O₄] – A Stuffed Variant of the K₂[Fe₂O₄] Type of Structure K₃[Fe₂O₄] has been obtained by tempering “Cs₃K₃CdO₄” in sealed Fe containers (36 d at 450–480 °C) as dark red transparent single crystals of rectangular shape. The structure determination (IPDS diffractometer data, MoKα, 1891 collected reflections, 234 symmetry independent, R1 = 0.033, wR2 = 0.088) confirms the space group Fddd; a = 596.11(9), b = 1140.3(1), c = 1717.9(3) pm; Z = 8. K₃[Fe₂O₄] exhibits a structure with [FeO₄] tetrahedra connected via corners leading to a three‐dimensional network closely related to the KFeO₂ type of structure. From the oxidation at 520 °C of iron metal with KO₂ in the presence of Na₂O black single crystal of K₂[Fe₂O₄] have been obtained. K₂[Fe₂O₄] crystallizes in the space group Pbca with Z = 8 and a = 559.18(7), b = 1122.1(1), c = 1592.8(2) pm (IPDS diffractometer data, MoKα, collected refelctions: 9543, 1213 symmetry independent, R1 = 0.043, wR2 = 0.102).